Crude oil refineries include an atmospheric pressure pipestill (APS) which fractionates the whole crude oil into various product fractions of different volatility, including gasoline, fuel oil, gas oil, and others. The lower boiling fractions, including naphtha, from which gasoline is derived, are recovered from the overhead fraction. The fractions with intermediate volatility are withdrawn from the tower as side streams. Side stream products include kerosene, jet fuel, diesel fuel, and gas oil. The higher up on the column the side stream is withdrawn, the more volatile the product. The heaviest components are withdrawn in the tower bottoms stream.
Stripping with steam is employed in atmospheric pipestills to strip bottoms and all side stream products (kerosene, diesel, gas oil). Without stripping, the typical pipestill, at best would be a poor fractionator. Steam stripping is used to adjust the front end of each liquid product to optimize the load to downstream processing, meet product specifications, or avoid downgrading a more valuable lighter product. Steam has historically been utilized as a stripping gas because it is available, inert and condensable and, thus, easily separated from hydrocarbons.
Several references teach the use of very small quantities of ammonia in a refinery including in pipestills. (See, for example, J59-102985; SU 1,147,734; U.S. Pat. No. 4,457,837; U.S. Pat. No. 4,486,299; and U.S. Pat. No. 5,326,482.)
The amounts of ammonia utilized in the above references are several fold less than the amounts required in the instant process.